Most of the alluvial areas of Pemali River Basin (DAS) in Brebes district are onion, soybean, cassava, and chili farm production centre. Besides, the area is also known for duck husbandry producing eggs, and it is developed fast. The agriculture and husbandry are mostly met in the residential area, whereas the activities use fertilizer and pesticides and also produce cattle waste which, of course, will contaminate people’s wells. Since the clean water service of the Municipal Waterworks (PDAM) has not reach all of the Pemali River Basin (DAS), especially in alluvial residential area, so for cooking, drinking, bathing, washing and other needs, the people make well with various depth, without concerning the right well making and health requirements. The purpose of the research is to map the quality of free ground water based on the depth of water ground surface in the Pemali DAS alluvial area. The method used is analyzing the quality of the free ground water laboratorically, and the result is plotted to 30 sample points in the map of groundwater surface depth divided into 11 classes. The result of the research shows that there are 10 parameters of water quality which content over the Limit Edge Value (NAB), they are, TDS, DHL, Organochlorine, Carbamat, Alkalinity, COD, BOD, Coliform Total, waste Coliform, and pH, whether the NO3-, NO2-, SO4=, Ca2+, phosphate, and muddiness parameter generally have content below NAB in all depth. Seen from some of the sample points which parameter amount has content over the NAB, the 0.37-3.98 meters ground water surface depth has eight parameters which over the NAB, then 0.10-0.36 meter depth with five parameters, and 3.99-8.50 meters with four parameters which over the NAB. Based on the parameter amount of each sample point, so in 0.37-1.27 meters MAT depth there are seven sample points where each sample has five water qualities which content over the NAB. The MAT depth showing good water quality according to the analysis is in the depth above 8.51 meters, and between 5.80-6.70 meters.